Long-Chain N -Acyl Amino Acid Synthases Are Linked to the Putative PEP-CTERM/Exosortase Protein-Sorting System in Gram-Negative Bacteria

Abstract

ABSTRACT Clones that encode the biosynthesis of long-chain N -acyl amino acids are frequently recovered from activity-based screens of soil metagenomic libraries. Members of a diverse set of enzymes referred to as N -acyl amino acid synthases are responsible for the production of all metagenome-derived N -acyl amino acids characterized to date. Based on the frequency at which N -acyl amino acid synthase genes have been identified from metagenomic samples, related genes are expected to be common throughout the global bacterial metagenome. Homologs of metagenome-derived N -acyl amino acid synthase genes are scarce, however, within the sequenced genomes of cultured bacterial species. Toward the goal of understanding the role(s) played by N -acyl amino acids in environmental bacteria, we looked for conserved genetic features that are positionally linked to metagenome-derived N -acyl amino acid synthase genes. This analysis revealed that N -acyl amino acid synthase genes are frequently found adjacent to genes predicted to encode PEP-CTERM motif-containing proteins and, in some cases, other conserved elements of the PEP-CTERM/exosortase system. Although relatively little is known about the PEP-CTERM/exosortase system, its core components are believed to represent the putative Gram-negative equivalent of the LPXTG/sortase protein-sorting system of Gram-positive bacteria. During the course of this investigation, we were able to provide evidence that an uncharacterized family of hypothetical acyltransferases, which had previously been linked to the PEP-CTERM/exosortase system by bioinformatics, is a new family of N -acyl amino acid synthases that is widely distributed among the PEP-CTERM/exosortase system-containing Proteobacteria .